1. Field of the Invention
The invention relates to reciprocating impact tools such as rammers and breakers and, more particularly, to a reciprocating impact tool powered by a two-cycle engine which has a lube oil supply system for transferring lubricating oil to a fuel supply line of the engine. The invention additionally relates to a method of operating such an impact tool and a method for its assembly.
2. Discussion of the Related Art
Reciprocating impact tools are used in a variety of compacting and breaking applications. The typical reciprocating impact tool includes an impacting member that is driven by a dedicated engine to impact against the ground to perform the desired function. Examples of reciprocating impact tools of this type are rammers and breakers. In a rammer, the impacting member comprises a pad or shoe that is driven to vertically reciprocate against the ground to compact it in preparation for a paving operation or the like. In a breaker, the impacting member comprises a bar or hammer that is driven to vertically reciprocate against the ground to fracture pavement or the like. The impacting member of each type of tool is typically driven by an eccentric crank that, in turn, is driven by a clutch and a gear train coupled to the tool""s engine.
Many reciprocating impact tools are powered by two-cycle engines. Two-cycle engines have the advantage of exhibiting a very high power-to-weight ratio, hence permitting the use of relatively powerful engines on tools that can be manually operated and manually transported. However, they have the potential disadvantage of being fueled by a gasoline/lubricating oil mixture rather than straight gasoline. The gasoline and oil are premixed and stored in the engine""s fuel tank. Proper operation of the engine depends upon the operator""s ability or willingness to properly premix the gasoline and lubricating oil in the tank. If too little oil is premixed with the gasoline, the engine is inadequately lubricated, can overheat, and may wear rapidly or even fail. If too much oil is premixed with the gasoline, engine performance is degraded and emissions are increased. This problem is serious because the gasoline and oil often are mixed in the field under less than optimal conditions. The operator may not have the proper equipment to measure the required quantities of gasoline and oil to obtain appropriate fuel oil ratios.
Attempts have been made to solve this problem by providing an oil injection system that injects a controlled quantity of lubricating oil into an engine""s fuel supply system, thereby negating the need to premix fuel and oil. The oil injection system includes an oil pump that transfers oil from an oil tank to the fuel supply system at a rate that results in the induction of an acceptable fuel/oil mixture into the engine""s combustion chamber(s). However, known attempts to eliminate the need to premix fuel and oil have met with only partial success.
For instance, one known vibratory rammer injects lubricating oil into a carburetor adapter attaching the engine""s carburetor to the engine block. Oil injected at this location is dispersed with the atomized air/fuel mixture in the carburetor just before the resultant air/fuel/oil mixture enters the engine""s combustion chamber through the intake port. The recently dispersed oil does not have an opportunity to be thoroughly atomized prior to being mixed with air and inducted into the engine""s combustion chamber. As a result, the lubricating qualities of the oil are reduced, and the oil does not burn as completely as it would if the oil were adequately atomized prior to its combustion. This lack of complete combustion reduces the engine""s efficiency, increases its emissions, and leads to a buildup of carbon deposits inside the engine""s combustion chamber and exhaust port.
Another problem associated with the above-described rammer is that it is relatively invasive. Its pump is driven directly by the engine""s drive shaft. The existing engine crankcase as supplied by the engine manufacturer must be modified significantly to accommodate the pump. This requirement to modify an engine crankcase to permit post-engine-manufacturing mounting of the pump in the crankcase substantially increases the overall cost and complexity of the rammer.
The need therefore has arisen to provide an oil supply system for a two-cycle engine of a reciprocating impact tool, such as a rammer or a breaker, that injects lubricating oil into the engine""s fuel supply system so as to assure good atomization of the oil prior to induction of the fuel/oil mixture into the combustion chamber(s) of the engine.
The need has also arisen to provide an oil injection system for a two-cycle engine of a reciprocating impact tool that requires no modifications to the existing engine crankcase.
In accordance with a first aspect of the invention, at least some of the above-identified needs, are satisfied by providing a reciprocating impacting machine comprising a two-cycle engine and a reciprocating impact tool. The engine includes a cylinder which has an intake port, a rotatable output shaft which is coupled to the cylinder, a fuel supply system, and an oil supply system. The fuel supply system includes a fuel tank, a fuel supply device that supplies a mixture of fuel and oil to the cylinder, and a fuel supply line leading from the fuel tank to the fuel supply device. The oil supply system supplies the lubricating oil to the fuel supply device. It includes an oil source, an oil supply pump having an oil inlet connected to the oil source and having an oil outlet, and an oil supply line connecting the oil outlet of the oil supply pump to the fuel supply line. The reciprocating impact tool is coupled to the engine output shaft and reciprocates against the ground upon engine output shaft rotation. The impact tool, the fuel supply system, and the oil supply system are configured such that operation of the reciprocating impact tool agitates oil in the fuel supply line sufficiently to thoroughly mix the oil in the fuel supply line with the fuel in the fuel supply line.
In order to reduce the build-up of carbon deposits in the engine""s combustion chamber(s) and exhaust port(s), the oil preferably is supplied only when the impact tool is operating. In order to achieve this effect, a centrifugal clutch may couple the engine output shaft to the oil supply pump and the reciprocating impact tool so that the oil supply pump is only operated when the engine RPM exceeds a designated threshold. In this case, the pump may be driven by the same drive gear that drives the reciprocating impact tool.
In order to maximize the agitation effects of machine operation on fuel and oil in the fuel supply line, the fuel supply line may comprise a flexible supply line, and the oil supply line may be coupled to the fuel supply line at a location which is remote from the fuel supply device. This spacing should be at least 6xe2x80x3.
In accordance with another aspect of the invention, a method of fueling a reciprocating impact machine comprises supplying a fuel/oil mixture to a supply device of a two-stroke engine by feeding fuel into the fuel supply line from the fuel tank, pumping oil from the oil source to the fuel supply line, and thoroughly mixing oil with fuel in the fuel supply line to form the fuel/oil mixture by agitating at least a substantial portion of the fuel supply line that includes the fuel/oil mixture. The agitating step results at least in substantial part by operation of the reciprocating impact tool.
In order to avoid carbon build-up in the engine""s combustion chamber and exhaust port by supplying lube oil when it is unnecessary to do so, the pumping step preferably is performed only at engine speeds above a designated engine speed.
In accordance with still another aspect of the invention, an improved method of assembling a reciprocating impact tool comprises providing 1) an engine crankcase that supports a cylinder, a fuel tank, a fuel supply device coupled to the cylinder, and a fuel supply line leading from the fuel tank to the fuel supply device and an input element of a centrifugal clutch, and 2) a tool crankcase that supports a reciprocatable impact tool, an oil supply pump, and an output element of the centrifugal clutch. Subsequent steps include connecting the engine crankcase to the tool crankcase and connecting one end of an oil supply line to an output of the oil supply pump and another end of the oil supply line to the fuel supply line at a location remote from the fuel supply device.
These and other objects, advantages, and features of the invention will become apparent to those skilled in the art from the detailed description and the accompanying drawings. It should be understood, however, that the detailed description and accompanying drawings, while indicating preferred embodiments of the present invention, are given by way of illustration and no t of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.